1. Field of the Invention
The present invention relates to an optical element, as well as a polarized-light-emitting surface light source and a display device using the same. Particularly, the present invention relates to an optical element that is capable of allowing light, which results from excitation by incident light, to be emitted through at least one of opposite sides of the optical element in the form of linearly polarized light having a certain plane of vibration, as well as a polarized-light-emitting surface light source using the optical element and a display unit using the polarized-light-emitting surface light source.
2. Discussion of the Background
As a light-guiding plate used in a so-called backlight of a liquid crystal display, a light emitting means, which is made up of a transparent resin plate and high-reflectance pigments such as titanium oxide or barium sulfate contained therein, is known. This light-guiding means emits light through one of the opposite sides of the transparent resin plate by scattering light, which is transmitted in the transparent resin plate upon total internal reflection.
The light emitted from the light-guiding plate having the above arrangement is natural light that exhibits almost no polarization characteristics. Therefore, it is necessary to convert natural light into linearly polarized light via a polarizing plate when it is used for a liquid crystal display. This conversion causes absorption loss of light by the polarizing plate, and hence causes a problem that the utilization rate of light cannot exceed 50%.
In order to address the above problem or achieve increased utilization rate of light, various backlights such as those employing a polarization splitter means that produces linearly polarized light by utilizing a so-called Brewster's angle, or those employing a retardation plate are proposed such as in Japanese Patent Application Laid-open Nos. Hei-6-18873, Hei-6-160840, Hei-6-265892, Hei-7-72475, Hei-7-261122, Hei-7-270792, Hei-9-54556, Hei-9-105933, Hei-9-138406, Hei-9-152604, Hei-9-293406, Hei-9-326205 and Hei-10-78581.
While addressing some problems, those conventional backlights still cannot attain sufficient polarization and are hard to control the polarization direction. As a result, they are of little practical use.
In consideration of the above problems, it is an object of the present invention to provide an optical element that is capable of allowing light, which results from excitation by incident light, to be emitted through at least one of the opposite aides of the optical element in the form of linearly polarized light having a certain plane of vibration, while optionally controlling the polarization direction (plane of vibration), as well as a polarized-light-emitting surface light source and a display device using this optical element.